1. Technical Field
The present disclosure relates generally to microelectronic elements and their fabrication. In particular, the present disclosure relates to a trench memory having self-aligned strap formed by self-limiting recess.
2. Description of Related Art
Deep trench capacitors have extensively been used in various microelectronic elements such as dynamic random access memory (DRAM) or embedded DRAM (eDRAM). A DRAM includes a capacitor for storing charge and a pass transistor (also called a pass gate or access transistor) for transferring charge to and from the capacitor. Data (i.e. 1 bit) stored in the cell is determined by the absence or presence of charge on the storage capacitor. The pass transistor and the trench capacitor are electrically connected through a strap—a portion of conductive material in the trench. During the fabrication of these and other devices, deep trenches are formed in a semiconductor substrate and then filled with a material such as, for example, polysilicon (poly). The material filling the trenches is subsequently recessed to a given depth below a major surface of the substrate.
In order to form an electrical connection between the transistor and the capacitor in a DRAM device, a uniform recess of the poly is necessary. However, it has proven particularly challenging to uniformly recess the poly to a predetermined depth with great precision within millions or even billions of trenches across a semiconductor wafer. The challenge is partially due to variation in the thickness of the deposited poly across the wafer, partially due to the variation in the trench size, and partially due to the variation in recessing process.
In light of the aforementioned difficulties of the processes used to recess materials within trenches, it would be desirable to provide a novel structure and methods of forming a precise and uniform recess depth of a trench poly for forming a trench memory device.